Philosophers Index AbstractThe essay addresses central themes of McMahan's The Ethics of Killing and Boonin's A Defense of Abortion1. The most general theme is that philosophical argument can settle some of the "marginal cases"--issues concerning contestable moral status and/or the boundaries of our existence. McMahan provocatively argues that personal identity theory can illuminate these issues. I reject McMahan's account of identity while endorsing his account of what matters2 in survival. I also contend that, suitably combined (and modified), McMahan's and Boonin's arguments greatly advance a liberal approach to abortion3. Finally, I address the definition of death and the authority of advance directives in dementia cases, with special attention to personal identity theory.